What’s going on with Bodhi?

Onyx Storm spoiler below

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In Imogen’s POV at the end of OS it says that Bodhi is on his hands and knees retching. This implies that he’s close to burnout, but how can he be?! His signet counters other signets and we know from the interaction with Theophanie that it doesn’t work against venin. So how can he be close to burnout? There would be no point in him wielding against the venin. Did he keep trying even though he knew it was pointless? Is there a second signet we don’t know about? If he’s the brother, did he turn so he could counter venin signets? So many questions.